You should enter the allowed amount in box 1. Form 1098 is more of a reporting requirement, but there's also a box to check if the interest amount you entered is different than on the 1098. On the next screen you'll be able to explain that the limitation applied. See the attached screenshots.
If you click the 'Learn more' blue hyperlink next to box 1, you'll find these instructions. As the instructions state, refer to IRS Publication 936 HERE and look for Table 1, Deductible Home Mortgage Interest, if you need assistance on calculating the amount.